Surveillance data from the field's best monitoring systems are detecting alarming increases in the rates of "club drug use" among young adults; yet, we know little about club drug abuse and dependence. Such information is essential to a relevant public health response. The proposed "Tri-City Study" will be the first study of the applicability, reliability and validity of abuse and dependence concepts as they apply to specific "club drugs." Specifically, a multisite study is proposed among 450 recent Ecstasy and other club drug users, 15 to 30 years of age, in areas indicated by NIDA's Community Epidemiology Workgroup (CEWG) as emerging or current areas of high risk -- St. Louis, Seattle and Miami -- to: 1) Describe the nature and extent of self-reported dependence on and abuse of Ecstasy, GHB, rohypnol and ketamine. This will be accomplished by determining whether "cookie cutter" diagnostic criteria used for other illicit drugs (such as described in DSM-IV, III-R, III, and ICD-10 and the Edwards-Gross Dependence Syndrome) are generalizable to individual club drugs, and to what extent users report the hallmark symptoms of dependence and abuse such as tolerance, withdrawal, craving, loss of control and social consequences; 2) a) Expand the Substance Abuse Module (SAM) to assess abuse of and dependence on specific club drugs and b) determine the psychometric properties (reliability and validity) of these disorders; 3) Understand the reasons for inconsistent answers and misunderstood questions; 4) Develop and test a Risk Behavior Assessment to facilitate the collection of risk factor data relevant to club drug use, abuse and dependence; 5) Conduct qualitative research on the unique contextual factors that relate to club drug use, in each site, to help inform revisions to the SAM and the RBA; 6) Disseminate the aggregate findings to the drug abuse field. Such efforts, considered mundane to many in the drug abuse field, are critical at this early stage of the club drug epidemic.